The saguaro (Carnegiea gigantea) cactus with its uplifted arms is an iconic symbol of the Southwestern Deserts. Occasionally (I read estimates ranging from 1 in 10,000 to 1 in 200,000) saguaro grow with the tip producing fan-like forms, or variations thereof. These saguaro are called crested or cristate.
These relatively rare growths form when cells in the growing tip (meristem) divide along a lateral rather than the usual radially symmetrical pattern of a normal stem. There is no consensus as to why this happens. A genetic mutation that may or may not require an external stimulus, lightning, frost or freezing temperatures and hormonal imbalance are a few of the suggested causes.
Many saguaro return to normal growth after years of cresting. (A new, uncrested arm is visible in one photograph.) Cristate saguaro still produce viable flowers and fruit and do not appear to be stunted by the cresting.
Cresting can happen in other cactus species, as well as some other plants.
These crests are on a huge saguaro near Green Valley AZ. This particular saguaro is locally famous and is fondly referred to as “Goliath”.
An earlier post (“Saguaro” on 06-08-16) provides more information on this cactus species.
No matter what the cause, cristate saguaro are fascinating and beautiful in their own way.